Disclosed are multicomponent fibers which include a surface modified thermobondable non-biodegradable synthetic polymeric component and a biodegradable component. The surface modified thermobondable non-biodegradable component permits thermal bonding of the multicomponent fiber to other fibers with enhanced adhesion. The multicomponent fibers are useful in the manufacture of nonwoven structures, and in particular nonwoven structures used as a component in disposable absorbent products.

The present invention relates to heat bondable multicomponent fibers, and more particularly heat bondable multicomponent fibers having a biodegradable polymeric component, as well as articles incorporating the fibers as a component thereof.
Synthetic fibers are widely used in a number of diverse applications to provide stronger, thinner, and lighter weight products. Synthetic fibers are typically heat adhesive (thermobondable) and thus are particularly attractive for the manufacture of nonwoven fabrics. Nonwoven fabrics, in turn, are widely used as components of a variety of articles, including without limitation absorbent personal care products, such as diapers, incontinence pads, feminine hygiene products, and the like; medical products, such as surgical drapes, sterile wraps, and the like; filtration devices; interlinings; wipes; furniture and bedding construction; apparel; insulation; and others.
Nonwoven fabrics can be formed entirely of synthetic fibers or a mixture of synthetic and natural fibers (such as cellulosic fibers). For example, typically disposable absorbent products include an absorbent core formed of cellulosic fluff pulp. The absorbent core can also include thermobondable synthetic fibers to thermally bind the cellulose fibers together, thereby achieving an absorbent material with improved strength. The product can also be thinner and lighter weight than traditional products.
Despite these advantages, the use of synthetic fibers in conjunction with cellulosic fluff pulp has not been without problems. For example, due to the non-polar, hydrophobic nature of conventional thermobondable fibers, the fibers can form conglomerations in the aqueous fluff pulp solution utilized during wet processing. Dry laid production of nonwovens using synthetic fibers can be difficult as well because of the lack of reactive sites on the surface of conventional thermobondable fibers. This results in a physical bonding, based on encapsulation, rather than chemical bonding. Even physical bonding is inherently difficult because of the non-polar nature of many synthetic fibers, which prevents the polymer from readily wetting out the surfaces of more polar fibers (such as cellulose fibers).
In addition, conventional synthetic fibers do not naturally degrade, thus creating problems associated with the disposal of products containing such fibers. In particular, recycling articles containing a blend of natural and conventional synthetic fibers is generally not cost effective, yet the disposal of these articles in landfills generates significant amounts of non-degradable waste. As landfills reach their capacity, the demand has increased for the incorporation of more degradable components in disposable products, as well as the design of products that can be disposed of by means other than by incorporation into solid waste disposal facilities.
To address concern over the issue of solid waste disposal, biodegradable polymers are increasingly used as a replacement for conventional synthetic polymers. Biodegradable polymers of interest include water-soluble polymers such as polyvinyl alcohol; naturally synthesized polymers such as sodium alginate and microbial polyesters; hydrolyzable aliphatic polyester and polyurethane polymers; and the like. Synthetic biodegradable aliphatic polyesters include polyglycolide and poly(lactic)acid polymers. See, for example, U.S. Pat. Nos. 5,166,231; 5,506,041; 5,759,569; and 5,171,309.
Of particular interest is the use of lactic acid to manufacture biodegradable resin. Poly(lactic)acid (hereinafter xe2x80x9cPLAxe2x80x9d) was initially introduced as a biodegradable polymer for medical products. U.S. Pat. Nos. 5,142,023 and 5,807,973 to Gruber et al. disclose processes by which a nonmedical grade of poly(lactic)acid may be produced and utilized in nonwoven fabrics. Examples of biodegradable fibers comprised entirely of polylactic acid polymers and/or copolymers are found in U.S. Pat. Nos. 5,010,145 and 5,760,144. See also U.S. Pat. Nos. 5,698,322 and 5,593,778 (directed bicomponent fibers which include poly(lactic acid) components).
The successful inclusion of biodegradable materials in disposable absorbent products provides several avenues by which these products may be discarded once their useful life has ended. Primarily, these articles may be easily and efficiently disposed of by composting. Alternatively, the disposable absorbent product may be easily and efficiently disposed of to a liquid sewage system wherein the disposable absorbent product is capable of being degraded.
Although biodegradable fibers are known, problems have been encountered with their use, for example, lack of control of the onset of polymer degradation. It is essential that biodegradable fiber maintain its integrity until its useful life has ended. U.S. Pat. No. 5,593,778 is directed to a core/sheath bicomponent fiber comprised entirely of poly(lactic acid), wherein the core PLA component biodegrades at a faster rate than the sheath. Although such fibers can provide some benefits, such fibers merely delay the onset of degradation and do not provide means for proactively controlling or initiating degradation of biodegradable fibers.
The present invention provides multicomponent heat adhesive or thermobondable fibers which exhibit a number of desirable, yet contradictory, properties in a single fiber structure. The fibers of the invention include a biodegradable polymeric component, thereby providing advantages in the disposal of products made with such fibers. However, in contrast to prior biodegradable fiber constructions, the fibers of the invention are structured so that initiation of degradation can be readily controlled.
In this regard, in addition to a biodegradable component, the fibers of the invention also include a thermobondable non-biodegradable polymeric component. The non-biodegradable polymeric component forms at least a portion of the exposed outer surface of the fibers, and in a preferred embodiment, completely encapsulates the biodegradable component. To control fiber degradation, the non-biodegradable polymer and biodegradable polymer can be selected so that the non-biodegradable polymer has a lower melting point (preferably at least about 10xc2x0 C. lower) than the melting point of the biodegradable polymer. The fibers can accordingly be thermally treated to melt away at least a portion of the non-biodegradable polymer component to expose the biodegradable component to conditions necessary to initiate decomposition or degradation thereof. Thus the fiber degradation process can be proactively initiated, rather than merely slowed or delayed, by protecting the biodegradable component from the environment until such a time as its degradation is purposefully triggered.
In addition, because the fibers of the invention include a thermobondable polymeric component on at least a portion of the exposed surface thereof, the fibers have useful thermobonding properties, with one another and/or with different fibers. Yet in contrast to conventional thermobondable fibers, the fibers of the invention can also have useful surface properties to assist in bonding to other types of fibers (such as cellulosic fibers). As discussed above, conventional thermobondable synthetic polymeric fibers are essentially hydrophobic and lack reactive polar sites on the surface thereof. Thus it can be difficult to effectively bond such fibers with more polar fibers, such as cellulosic fibers.
In the invention, the surface properties of the thermobondable non-biodegradable polymeric component are modified using a surface active agent. In a preferred embodiment of the invention, the thermobondable non-biodegradable polymeric component includes maleic acid or maleic anhydride which adds polar groups to the surface of the fibers and imparts hydrophilic properties thereto. Biodegradable polymers typically have some polarity as compared to conventional thermoplastic polymers, such as polyester and nylon. The grafted binder thus can exhibit improved adhesion to the biodegradable component as well. The maleic acid or anhydride can be blended with or grafted onto the polymer. Thus the modified thermobondable non-biodegradable polymeric component provides both thermal bonding capability and enhanced adhesion as compared to conventional heat bondable polymers. As a result, the fibers of the invention are particularly useful in the production of nonwoven fabrics, including those used in disposable absorbent articles, such as absorbent webs formed of cellulosic fluff.
The present invention also provides fabrics formed of the multicomponent fibers of the invention, articles incorporating such fabrics as a component, processes for making the fibers and processes for controlling the degradation of articles made using the fibers.
The present invention will be described more fully hereinafter in connection with illustrative embodiments of the invention which are given so that the present disclosure will be thorough and complete and will fully convey the scope of the invention to those skilled in the art. However, it is to be understood that this invention may be embodied in many different forms and should not be construed as being limited to the specific embodiments described and illustrated herein. Although specific terms are used in the following description, these terms are merely for purposes of illustration and are not intended to define or limit the scope of the invention.
The multicomponent fibers of the invention include at least two structured polymeric components, a thermobondable non-biodegradable synthetic polymeric component and a biodegradable polymeric component. Multicomponent fibers are formed of two or more polymeric materials. For purposes of illustration only, the present invention will generally be described in terms of a bicomponent fiber comprising two components. However, it should be understood that the scope of the present invention is meant to include fibers with two or more components.
In general, the components are arranged in substantially constantly positioned distinct zones across the cross section of the multicomponent fiber and extend continuously along the length of the multicomponent fiber. A preferred configuration is a sheath/core arrangement, wherein a first component, the sheath, substantially surrounds a second component, the core. However, other structured fiber configurations as known in the art may potentially be used, such as but not limited to, xe2x80x9cislands-in-the-seaxe2x80x9d arrangements, segmented cross sections and the like. Reference is made to U.S. Pat. No. 5,108,820 to Kaneko et al., U.S. Pat. No. 5,336,552 to Strack et al., and U.S. Pat. No. 5,382,400 to Pike et al. for a further discussion of multicomponent fiber constructions. The multicomponent fibers may also have unconventional shapes (such as multi-lobal) such as described in U.S. Pat. No. 5,277,976 to Hogle et al., and U.S. Pat. Nos. 5.057,368 and 5,069,970 to Largman et al.
The cross section of the multicomponent fiber is preferably circular, since the equipment typically used in the production of multicomponent synthetic fibers normally produces fibers with a substantially circular cross section. The configuration of the first and second components in a fiber of circular cross section can be either concentric or acentric, the latter configuration sometimes being known as a xe2x80x9cmodified side-by-sidexe2x80x9d or an xe2x80x9ceccentricxe2x80x9d multicomponent fiber.
The concentric configuration is characterized by the first component having a substantially uniform thickness, such that the second component lies approximately in the center of the fiber. In the acentric configuration, the thickness of the first component varies, and the second component therefore does not lie in the center of the fiber. In either case, the second component is substantially surrounded by the first component. However, in an acentric bicomponent fiber, a portion of the second component may be exposed, such that in practice up to about 20% of the surface of the fiber may be comprised of the second component. The first component in a fiber with an acentric configuration will nevertheless comprise the major part of the surface of the fiber, i.e., at least about 80%. Both the cross section of the fiber and the configuration of the components will depend upon the equipment which is used in the preparation of the fiber, the process conditions and the melt viscosities of the two components.
The thermobondable (or heat adhesive) non-biodegradable polymeric component advantageously has a lower melting point relative to the melting point of the biodegradable polymeric component so that the thermobondable non-biodegradable polymeric component can act as a latent adhesive. Thermal bonding is a well-known method of nonwoven fabric formation in which synthetic fibers are heated to their glass transition point or beyond, causing the fibers to soften and adhere to adjoining fibers, thereby forming a nonwoven fabric. Preferably the thermobondable non-biodegradable polymeric has a melting or softening point of at least 10xc2x0 C., more preferably at least about 20xc2x0 C., and most preferably at least about 25xc2x0 C., less than the melting point of the biodegradable polymeric component.
In addition, the thermobondable non-biodegradable synthetic polymeric component includes a surface active agent to modify the surface properties of the polymer (i.e., to impart hydrophilicity thereto). Because the surface properties of the polymer have been modified, the fibers can exhibit improved adhesion, particularly with fibers having polar surfaces (such as cellulosic fibers). The modified surface of the thermobondable polymeric component is also thought to provide improved adhesion between the components of the multicomponent fiber itself.
Preferred polymers for use in the thermobondable non-biodegradable polymeric component are polyolefins, and in particular, long-chain, synthetic polymers of at least 85 weight percent ethylene, propylene or other olefin unit. Suitable polyolefins include polyproylene, polyethylene, polybutene, and copolymers and mixtures thereof Specific examples of polyolefins suitable for use in the thermobondable non-biodegradable component include high density polyethylene, low density polyethylene, linear low density polyethylene, poly(1-butene), polypropylene, and copolymers, terpolymers, and mixtures thereof. In addition, the thermobondable non-biodegradable polymeric component may include mixtures of polyolefins with other polymers, such as but not limited to (ethyl vinyl acetate) copolymers, (ethylene acrylic acid) copolymers, and the like. Preferably the polyolefin is a polyethylene, in particular high density polyethylene. Other suitable polymers include polystyrenes, polyurethanes, acetal resins, and copolymers, terpolymers, and mixtures thereof. In addition, polyester copolymers and polyamide copolymers may also be used.
Surface active agents suitable for the present invention include alpha, beta unsaturated carboxylic acids capable of participation in a polymer grafting reaction. In a preferred embodiment, maleic acid or maleic anhydride is grafted onto the thermobondable non-biodegradable polymer, thereby incorporating succininc acid or anhydride groups into the polymer structure.
The grafting of succininc acid or succininc anhydride groups may be done by methods described in the art which generally involve reacting maleic acid or maleic anhydride in admixture with heated polymer, generally using a peroxide or free radical initiator to accelerate the grafting. The maleic acid and maleic anhydride compounds are known to have olefin unsaturation sites conjugated to the acid groups. Fumaric acid, an isomer of maleic acid which is also conjugated, gives off water and rearranges to form maleic anhydride when heated, and is thus operable in the present invention. Grafting may be effected in the presence of oxygen, air, hydroperoxides, or other free radical initiators, or in the essential absence of these materials when the mixture of monomer and polymer is maintained under high shear and heat conditions. See, for example, U.S. Pat. Nos. 5,167,765; 5,372,885; and 4,950,541, the entire disclosure of each of which is hereby incorporated by reference.
The anhydride or acid groups of the grafted polymer generally comprise from about 0.001 to about 10 weight percent, preferably from about 0.01 to about 5 weight percent, and more preferably from 0.1 to about 1 weight percent of the grafted polymer. The grafted polymer is characterized by the presence of pendantsuccinic acid or anhydride groups along the polymer chain, as opposed to the carboxylic acid groups obtained by the bulk copolymerization of ethylene with an alpha, beta ethylenically unsaturated carboxylic acid such as acrylic acid.
The thermobondable non-biodegradable polymeric component may include the grafted polymer singly or as a component of a polymer blend. Polymers useful in such a polymer blend include the polyolefins noted above. When a blend is used, the polymer blend can contain from about 0.5 to about 99.5 weight percent of grafted polymer, preferably from about 1 to 50 weight percent grafted polymer, and more preferably from about 2 to 15 weight percent grafted polymer. See U.S. Pat. No. 5,372,885. See also U.S. Pat. Nos. 5,185,199; 5,126,199; and 5,082,899, the entire disclosure of each of which is also incorporated by reference.
The second component of the fibers of the invention includes a biodegradable polymer as known in the art. As used herein, xe2x80x9cbiodegradablexe2x80x9d refers to a material that degrades under aerobic and/or anaerobic conditions in the presence of bacteria, fungi, algae, and other microorganisms to carbon dioxide/methane, water and biomass, although materials containing heteroatoms can also yield other products such as ammonia or sulfur dioxide. xe2x80x9cBiomassxe2x80x9d generally refers to the portion of the metabolized materials incorporated into the cellular structure of the organisms present or converted to humus fractions indistinguishable from material of biological origin. As a result, the biodegradable fiber, either in its initial form or after incorporation into a fabric, will begin to degrade when exposed to such microorganisms, even if such exposure occurs prior to the expiration of the fiber""s useful life. Exemplary biodegradable polymers include, without limitation, polyvinyl alcohol, hydrolyzable aliphatic polyesters, hydrolyzable aliphatic polyurethanes, cis-polyisoprene, cis-polybutadiene, poly(caprolactone), hydrolyzable poly(lactic acid), poly(hydroxy alkanoates), and the like and copolymers and blends thereof. As the skilled artisan will appreciate, poly(lactic acid) is hydrolyzed before it can be consumed by microorganisms.
The biodegradable polymeric component can also be selected to provide strength or rigidity to the fiber and, thus, to nonwoven structures comprising the multicomponent fiber. Strength or rigidity of the fiber is generally achieved by selecting biodegradable component having a thermal melting temperature greater than the thermal melting temperature of the thermobondable non-biodegradable component. As a result, when the multicomponent fiber is subjected to an appropriate temperature, typically near the melting temperature of the first non-biodegradable component but less than the melting temperature of the second biodegradable component, the first component will soften while the second component will generally maintain its rigid form.
Preferably the biodegradable polymeric component comprises poly(lactic acid). In addition to biodegradability, poly(lactic acid) can impart other desirable properties to the fibers of the invention. For example, the fibers of the invention which include poly(lactic acid) as a component can exhibit improved tensile strength, as compared to fibers including polyethylene terephthalate or polyamides as a high temperature core. Further, it is believed that the fibers can exhibit improved adhesion between the polymeric components when poly(lactic acid) is used, as compared to polyethylene terephthalate and/or polyamides.
Poly(lactic acid) polymer is a biodegradable polyester polymer generally prepared by the polymerization of lactic acid. However, it will be recognized by one skilled in the art that a chemically equivalent material may also be prepared by the polymerization of lactide. Therefore, as used herein, the term xe2x80x9cpoly(lactic acid) polymerxe2x80x9d is intended to represent the polymer that is prepared by either the polymerization of lactic acid or lactide. Reference is made to U.S. Pat. Nos. 5,698,322; 5,142,023; 5,760,144; 5,593,778; 5,807,973; and 5,010,145, the entire disclosure of each of which is hereby incorporated by reference.
Lactic acid and lactide are known to be an asymmetrical molecules, having two optical isomers referred to, respectively as the levorotatory (hereinafter referred to as xe2x80x9cLxe2x80x9d) enantiomer and the dextrorotatory (hereinafter referred to as xe2x80x9cDxe2x80x9d) enantiomer. As a result, by polymerizing a particular enantiomer or by using a mixture of the two enantiomers, it is possible to prepare polymers that are chemically similar yet which have widely differing properties. In particular, it has been found that by modifying the stereochemistry of a poly(lactic acid) polymer, it is possible to control the melting temperature of the polymer.
The degree of crystallinity of a PLA polymer is based on the regularity of the polymer backbone and its ability to line up with similarly shaped sections of itself or other chains. If even a relatively small amount of D-enantiomer (of either lactic acid or lactide), such as about 3 to about 4 weight percent, is copolymerized with L-enantiomer (of either lactic acid or lactide), the polymer backbone generally becomes irregularly shaped enough that it cannot line up and orient itself with other backbone segments of pure L-enantiomer polymer, thus reducing the crystallinity of the polymer, which in turn suppresses the melting point. Based on the foregoing, although a minimal amount of D-enantionmer can be tolerated, preferably the amount of D-enantiomer present in the instant invention is not such that it suppresses the melting point of the PLA component to the melting point of the first component, or to within 10xc2x0 C. thereof.
Advantageously the PLA polymer also exhibits residual monomer percents effective for the second component to exhibit desirable melt strength, fiber mechanical strength, and fiber spinning properties. As used herein, xe2x80x9cresidual monomer percentxe2x80x9d refers to the amount of lactic acid or lactide monomer that is unreacted yet which remains entrapped within the structure of the entangled PLA polymer chain. In general, if the residual monomer percent of a PLA polymer in a component is too high, the component may be difficult to process due to inconsistent processing properties caused by a large amount of monomer vapor being released during processing that cause variations in extrusion pressures. However, a minor amount of residual monomer in a PLA polymer in a component may be beneficial due to such residual monomer functioning as a plasticizer during a spinning process. Thus, the PLA polymer in the second component generally exhibits a residual monomer percent that is less than about 15 percent, preferably less than about 10 percent, and more preferably less than about 7 percent.
Each of the thermobondable non-biodegradable polymeric component and the biodegradable polymeric component can optionally include other components not adversely effecting the desired properties thereof. Exemplary materials which could be used as additional components would include, without limitation, pigments, antioxidants, stabilizers, surfactants, waxes, flow promoters, solid solvents, particulates, and other materials added to enhance processability of the first and the second components. For example, a stabilizing agent may be added to the biodegradable polymer to reduce thermal degradation which might otherwise occur during the poly(lactic) acid spinning process. The use of such stabilizing agents is disclosed in U.S. Pat. No. 5,807,973, hereby incorporated by reference. Further, additives which enhance the biodegradability of the poly(lactic)acid may optionally be included, as disclosed in U.S. Pat. No. 5,760,144, previously incorporated by reference. These and other additives can be used in conventional amounts.
The weight ratio of the thermobondable non-biodegradable polymeric component and the biodegradable polymeric component can vary. Preferably the weight ratio is in the range of about 10:90 to 90:10, more preferably from about 30:70 to about 70:30, and most preferably from about 40:60 to about 60:40.
As discussed above, the thermobondable non-biodegradable component generally provides an exposed surface on at least a portion of the multicomponent fiber, thereby permitting thermal bonding of the multicomponent fiber to other fibers (which may be the same or different from the multicomponent fiber of the present invention). Advantageously the thermobondable non-biodegradable polymeric component comprises at least about 25 percent, preferably at least about 40 percent, and more preferably at least about 60 percent, or more of the total surface area of the multicomponent fiber. In one preferred aspect of the invention, the thermobondable non-biodegradable polymeric component comprises 100 percent of the surface of the fiber (for example, the sheath of a sheath/core fiber). As a result, the multicomponent fiber is useful in the production of a wide variety of thermally bonded fibrous nonwoven structures, such as but not limited to carded webs, wet laid webs, dry laid webs, spunbonded webs, meltblown webs, and the like. While particularly useful in the production of nonwoven fabrics, the fibers of the invention can also be used to make other textile structures such as but not limited to woven and knit fabrics.
In addition, the onset of biodegradation in a multicomponent article containing a biodegradable polymer may be delayed until purposefully triggered, thereby extending the anticipated useful life of articles containing such biodegradable polymers. Therefore, in one aspect of the invention, fabric bonding occurs by simply softening the latent adhesive polymer without fully melting it, thereby leaving the latent adhesive polymer layer intact to protect the biodegradable polymer from the environment. Degradation of the fiber or article can then be initiated by a heat treatment of the fiber of the present invention, or article containing such fiber, prior to its disposal in the environment. This heat treatment is effected by exposing the fiber to sufficient energy to decrease the melt viscosity of the latent adhesive polymer so that it flows off of, or melts away from, the surface of the biodegradable polymer, thereby exposing the biodegradable polymer to the environment and triggering subsequent degradation.
In this aspect of the invention preferably the thermobondable non-biodegradable component comprises 100 percent of the surface of the fiber, thereby providing both thermal bonding properties and maximum protection to the biodegradable core. In this embodiment, a core/sheath structure is preferred. The core/sheath fiber can advantageously be incorporated into a thermally bonded nonwoven fabric, which can then be subjected to a heat treatment after the useful life of the fabric has ended.
In another aspect of this invention, the biodegradable polymer may be exposed to the environment during fabric formation. In this aspect, sufficient energy is supplied during the thermal bonding process to allow the latent adhesive polymer to flow off of the surface of the biodegradable polymer.
Methods for making multicomponent fibers are well known and need not be described here in detail. Generally, to form a multicomponent fiber, at least two polymers are extruded separately and fed into a polymer distribution system wherein the polymers are introduced into a segmented spinneret plate. The polymers follow separate paths to the fiber spinneret and are combined in a spinneret hole. The spinneret is configured so that the extrudate has the desired shape.
Following extrusion through the die, the resulting thin fluid strands, or filaments, remain in the molten state for some distance before they are solidified by cooling in a surrounding fluid medium, which may be chilled air blown through the strands. Once solidified, the filaments are taken up on a godet or another take-up surface. In a continuous filament process, the strands are taken up on a godet which draws down the thin fluid streams in proportion to the speed of the take-up godet. In the jet process, the strands are collected in a jet, such as for example, an air gun, and blown onto a take-up surface such as a roller or a moving belt to form a spunbond web. In the meltblown process, air is ejected at the surface of the spinnerette which serves to simultaneously draw down and cool the thin fluid streams as they are deposited on a take-up surface in the path of cooling air, thereby forming a fiber web. Regardless of the type of melt spinning procedure which is used, it is important that the thin fluid streams be melt drawn down in a molten state, i.e. before solidification occurs to orient the polymer molecules for good tenacity. Typical melt draw down ratios known in the art may be utilized. Where a continuous filament or staple process is employed, it may be desirable to draw the strands in the solid state with conventional drawing equipment, such as, for example, sequential godets operating at differential speeds. See, for example, U.S. Pat. No. 5,082,899.
Following drawing in the solid state, the continuous filaments may be crimped or texturized and cut into a desirable fiber length, thereby producing staple fiber. The length of the staple fibers generally ranges from about 25 to about 50 millimeters, although the fibers can be longer or shorter as desired. See, for example, U.S. Pat. No. 4,789,592 to Taniguchi et al. and U.S. Pat. No. 5,336,552 to Strack et al.
The use of poly(lactic)acid in composite fibers is especially advantageous. Poly(lactic)acid develops tensile properties which are comparable or improved in comparison to the polyester and polyamide polymers traditionally employed in the core of bicomponent binder fibers.
The multicomponent fibers of the invention can be staple fibers, continuous filaments, or meltblown fibers. In general, staple, multi-filament, and spunbond fibers formed in accordance with the present invention can have a fineness of about 0.5 to about 100 denier. Meltblown filaments can have a fineness of about 0.001 to about 10.0 denier. Monofilament fibers can have a fineness of about 50 to about 10,000 denier.
As noted above, the multicomponent fibers can be incorporated into a fabric. Fibers other than the multicomponent fibers of the invention may be present as well, including any of the various synthetic and/or natural fibers known in the art. Exemplary synthetic fibers include polyolefin, polyester, polyamide, acrylic, rayon, cellulose acetate, thermoplastic multicomponent fibers (such as conventional sheath/core fibers, for example polyethylene sheath/polyester core fibers) and the like and mixtures thereof. Exemplary natural fibers include wool, cotton, wood pulp fibers and the like and mixtures thereof. As noted above, because the fibers of the invention have modified surface properties, the fibers are particularly advantageous in combination with polar fibers, such as wood pulp fibers.
In a preferred embodiment, the multiconstituent fiber of the instant invention is incorporated into a nonwoven fabric. Staple fibers of the present invention may be formed into nonwoven webs by any means known in the art, including dry laid processes, such as carding or airlaying, as well as wet laid processes. Wet laid webs are of particular interest in the present invention, and such a process is described in U.S. Pat. Nos. 5,167,765 and 5,456,982, both hereby incorporated by reference. In addition, continuous filament may be spun directly into nonwoven webs by a spunbonding process.
Alternatively, in one embodiment of the present invention, the multicomponent fibers of the invention may be incorporated, alone or in conjunction with other fibers, into a meltblown nonwoven fabric. The technique of meltblowing is known in the art and is discussed in various patents, e.g., Buntin et al., U.S. Pat. No. 3,987,185; Buntin, U.S. Pat. No. 3,972,759; and McAmish et al., U.S. Pat. No. 4,622,259.
The nonwoven webs thus formed are typically subsequently thermally bonded to transform them into nonwoven fabrics, using any thermal bonding technique known in the art.
Nonwoven fabrics which include the multicomponent fibers of the invention as a component are particularly suited for use in disposable products. Specific examples include without limitation disposable diapers, adult incontinent products, sanitary napkins, tampons, wipes, bibs, wound dressings, and surgical capes or drapes.
The nonwoven fabrics of the invention are particularly advantageous as components of a disposable diaper. Disposable diapers typically include a liquid-permeable topsheet, a backsheet attached to the liquid-permeable topsheet, and an absorbent structure positioned between the liquid-permeable topsheet and the backsheet. The nonwoven fabrics of the invention may be incorporated into any of the components which make up the disposable absorbent product, but are preferably included in the absorbent structure. Such absorbent structures are typically multilayered, comprising at least one acquisition/distribution layer and at least one storage layer. The nonwoven fabrics of the invention are particularly useful as a component of the storage layer. Exemplary disposable absorbent products are generally described in U.S. Pat. Nos. 4,710,187; 4,762,521; 4,770,656; and 4,798,603.
The fabrics of the invention can also be used as a layer in composite fabric laminate. By combining two or more nonwoven fabrics of different types, nonwoven fabric laminates have been developed for a variety of specific end use applications. Specific examples of such fabrics are described in U.S. Pat. Nos. 3,676,242; 3,795,771; 4,041,203; 4,766,029 and 4,863,785.
The present invention will be further illustrated by the following non-limiting example.

Heat bondable biodegradable fibers with enhanced adhesion


An endoscope having an endoscope shaft at the distal end of which a solid state image-recording system is disposed which is designed in the manner of lateral-view optics.

1. Technical Field
The present invention relates to an endoscope having an endoscope shaft at the distal end of which is disposed a solid state image-recording system designed in the manner of lateral-view optics.
2. State of the Art
The surgical use of endoscopes has meanwhile proven to be quite successful and is in many cases, in addition to the conventional surgical techniques, a minimally invasive alternative procedure that has the advantage of being much less taxing to the patient and of shortening recovery time considerably. Apart from application in incorporal manipulation, respectively using suited endoscopic instruments for treatment of diseased parts of the body, endoscopes predominantly find use as a means of viewing and examining cavities in the human body.
In addition to the hitherto known, conventional rigid rod lens endoscopes, which only possess a single optical viewing channel and with which the surgeon receives only a two-dimensional image of the viewing area, there are known endoscopes that, using stereoscopic optical systems, permit reproduction of the surroundings of the surgery region including its spatial configuration.
The first considerations involving spatial viewing with the aid of endoscopes, the so-called stereo endoscopes, are based on the 1904 German patent DE 16 49 66, pertain to two separate, optical viewing paths which permit viewing an object opposite the distal end of the endoscope from two different directions. The proximal part of the endoscope is connected to a double eyepiece which simultaneously permits viewing the object with both eyes.
In addition to solely visual observation by the surgeon, for a number of reasons, it is desirable and even necessary in minimal-invasive endoscopic surgical techniques to realize the representation of the surgery area using video technology via a camera-monitor unit. Furthermore, the endoscopic procedure can be stored using video technology in such a manner that exact viewing is possible even following surgery. In this context, the described, conventional, optical stereo-endoscopic system requires that the two separate optical viewing systems each be connected at their proximal end to a camera system. These types of connection arrangements, however, in some instances demand very complex adjustments, therefore making handling the endoscope significantly more cumbersome. Moreover, the optical elements, respectively rod lenses in the endoscopes of the described, optical stereo systems possess a certain amount of mobility, which makes it impossible to prevent system-related blurriness at least not in adjusting the system.
As an alternative to conventional image transmission between the distal end and the proximal end of the endoscope with the aid of optical components (imaging lenses, optical fiber systems, i.a.), video image recorders, such as by way of illustration CCD-chips, are increasingly coming into use. For this reason, it has been often proposed to place in the image plane of the lenses disposed at the distal end of the endoscope an image recorder that is connected to a supply unit disposed at the proximal endoscope end by means of a transmission system instead of the conventional optical transmission systems. Concerning this, by way of example, reference is made to U.S. Pat. Nos. 4,235,447 and 4,261,344.
Therein solid state image-recording devices are widely employed, and of them the charge-coupled sensor types respectively CCD arrays seem to be the most suited.
Placing image-recording systems of this type at the distal end has the advantage, ie. that image transmission from the distal end to the proximal end of the endoscope can be carried out electronically, i.e., the signal transmission occurs via corresponding electric lines. This ensures more flexible endoscope guidance without optical distortions. Moreover, the considerable cost of the optical rod lenses is eliminated, permitting cheaper production of xe2x80x9celectronic viewing endoscopesxe2x80x9d.
U.S. Pat. Nos. 4,699,125 and 4,926,257 deal with such types of endoscopes at which distal end image-recording systems are provided which are essentially composed of a lens and a solid state image-recording element, preferably a CCD array.
Furthermore, comparable electronic endoscopes are described in the following printed publications: U.S. Pat. Nos. 5,050,584, and 4,989,586 as well as DE-OS 38 06 190.
In the mentioned endoscopes, a semiconductor image recorder is placed in the image plane of the lens disposed at the distal end in such a manner that the light-sensitive sensor area forms a 90xc2x0 angle with the axis of the endoscope. Reduction of the cross section of the endoscope in the distal region, therefore, is limited at least due to the currently smallest possible dimensioning of solid state image-recording sensors.
As an alternative to the so-called straight-ahead view endoscopes like the ones described in the mentioned state of the art, the lateral-view endoscopes having surface sensors which are aligned parallel to the axis of the endoscope offer major minimization of the cross section of the endoscope. Devices of this type are described in U.S. Pat. Nos. 4,685,451, and 4,562,831 as well as the German A-document DE 32 33 924. Lateral-view endoscopes whose view is aligned perpendicular to the axis of the endoscope and therefore are also aligned for insertion of the endoscope are primarily for gastroenterological viewing and examinaton of the duodenum and further treatment in the gall duct, which is practically at a 90xc2x0 angle to the duodenum. Although this construction reduces the cross section of the endoscope, the surgeon is unable to view the region into which the endoscope is inserted in the direction of movement.
Contrary to electronic endoscopes which only have a single image-recording system, the German A-document DE 38 06 190 describes electronic endoscopic devices each having two imaging devices which, using solid state image recorders, permit the surgeon to gain a spatial impression of the viewing region of the endoscope. Although placing the image-recording systems in pairs in the straight-ahead viewing direction at the distal end of the endoscope grants the surgeon a viewing region which lies immediately before the tip of the endoscope and therefore permits controlled movement of the endoscope into the inside of the body, due to the necessity of working with as small as possible endoscope diameters, the spacing of the image recorder systems, the so-called stereo base, selected cannot be very large. However, this diametrically opposes the possibility of increasing the spatial visual impression and therefore a large as possible stereo base. Moreover, while maintaining a small as possible endoscope diameter, solid state image sensors having very small dimensions and therefore worse resolution can be utilized in this arrangement.
DE 39 21 233.5 describes, among other things, in FIG. 4, an electronic stereo endoscope in straight-ahead viewing. For this purpose, two independently movable image-recording systems are pivoted out of the co-axial position laterally to the side of the endoscope in such a manner that the stereo base can be enlarged considerably. The laterally pivotable folding mechanism of both image-recording systems makes it possible to meet the requirement of having an as small as possible endoscope cross section. Although the proposed solution offers the surgeon a spatial impression of the viewing area in the straight-ahead direction, it does not allow further degrees of freedom. Moreover, the exact positioning of both recording systems in relation to each other is a source of problems.
The object of the present invention is to further improve an endoscope having an endoscope shaft at the end of which a solid state image-recording system is disposed which is designed in the manner of lateral-view optics in such a way that the most optimum possible spatial impression of a lateral field can be obtained with the smallest possible endoscope cross section. Furthermore, three-dimensional viewing should include as much of the whole cavity into which the stereo endoscope is inserted as possible. The surgeon should be given an as simple as possible to operate viewing tool that, by way of illustration, completely obviates the necessity of adjusting the optics during use and that largely simplifies handling in such a way that there is never any difficulty in spatial orientation. Moreover, as large as possible image sensors having respectively high image resolution should be employed.
The present invention is based on the fundamental idea that the distal end of a lateral-view endoscope that is provided with at least two image recorders assumes in one position the lateral viewing direction and in the second position the straight-ahead viewing direction. By changing the viewing direction of the image-recording system by at least 90xc2x0 C., the whole cavity can be viewed, by way of illustration, by additionally turning the endoscope about its longitudinal axis.
An element of the present invention is that the endoscope having a solid state image recording system, which is designed in the manner of lateral view optics, at its distal end is provided with at least two image recorders. In addition, the endoscope shaft can be deflected in the distal region in such a manner that the viewing direction of the solid state image-recording system can be aligned approximately parallel to the axis of the proximal part of the endoscope shaft. Another invented element is that the viewing direction of the solid state image-recording system can be disposed approximately coaxially to the axis of the proximal part of the endoscope shaft.
In other words, the overall inventive idea is to realize a stereo image-recording endoscope with a smallest possible endoscope shaft cross section for insertion into a cavity as well as to provide the largest possible stereo base while at the same time employing large-surface solid state image sensors with high resolution in order to ensure a distinct three-dimensional visual impression. The image-recording systems are provided in the distal region of the endoscope shaft in the lateral viewing direction in such a manner that the light-sensitive solid state image sensors are disposed in a row in the longitudinal axis of the endoscope. This has the advantage that the smallest cross section of the endoscope shaft is independent of both dimensions of an image sensor, but rather is only dependent on the lateral side of the sensor, thereby permitting as small as possible dimensioning of the endoscope cross section.
Once the endoscope has been inserted into the cavity to be viewed, according to the present invention, the viewing unit attached to the distal end of the endoscope can be switched from a lateral view direction to a second position which permits straight-ahead viewing. In order to make it easier for the surgeon to handle the endoscope, a defined change of position of the endoscope shaft from lateral view to straight-ahead view and vice-versa is provided. This factilitates handling considerably for the surgeon and simplifies coordination between the lateral-viewing direction and the straight-ahead direction. In this manner, orientation inside the cavitiy is improved by means of the two provided viewing-direction settings.
Of course, depending on the application, continuous movement of the endoscope shaft in several directions is also possible.
The present invention permits a viewing direction, which is disposed coaxially to the longitudinal axis of the endoscope, of the deflected endoscope shaft in the distal region in such a manner that, due to a 90xc2x0 deflection relative to the longitudinal axis of the endoscope, the solid state image-recording system is quasi foldable in the straight-ahead direction. The discrete deformation of the endoscope shaft can be executed with the aid of a component provided in the distal region of the endoscope shaft which preferably is composed of a material having a thermal or mechanical memory capacity. For this purpose, in the insertion step, the endoscope shaft, which is provided with a rigid and a flexible part, is inserted into the cavity through a longitudinal trocar tube. If the flexible part of the endoscope shaft in the cavity emerges from the trocar tube, it automatically assumes its prescribed shape which is provided in such a manner that the image-recording system is preferably oriented in the straight-ahead direction.
This deflection of the endoscope shaft in the distal region can also occur in a controlled manner by means of Bowden wires or controllable joints, which can be operated manually or via an engine provided in the flexible part of the endoscope shaft.
In addition to being able to deflect the endoscope shaft in the distal region 90xc2x0 permitting spatial viewing parallel to the longitudinal axis of the endoscope but not coaxially thereto, an element of the present invention is that it provides for another possible deflection of the endoscope shaft in the distal region which provides for viewing in spatial quality coaxially to the axis of the proximal part of the endoscope shaft.
The preceding viewing variant has the additional advantage that the surgeon receives a spatial visual impression of the viewing field through the endoscope which is immediately before the distal region in the thrust direction of the endoscope and therefore is largely coaxial to the longitudinal axis of the endoscope.
Handling the endoscope having a coaxial arrangement of the solid state image-recording system in the straight-ahead direction is similar to that of conventional rod lens endoscopes. This endoscopic solution obviates having to get accustomed to working with other imaging properties.
This distal arrangement of the solid state image-recording system is already advantageous with only one image recorder.
The use of stereo endoscopes of this type having an as large as possible stereo base for gaining an intensive spatial visual impression has the primary purpose of permitting the surgeon to improve his assessment of spatial distances. Especially, the handling of other endoscopic instruments for incorporal treatment in the vision cone of the stereo endoscope is decisively simplified by the spatiality of the visual impression. Thus, the surgeon is able to work with at least two instruments inserted into the cavity in such a manner as if the surgeon had a direct look at the to-be-treated site. Furthermore, absolute measurement can be taken with the invented stereo endoscope. In addition to the previously mentioned decisive improvement for controlled execution of complicated surgical techniques using endoscopic instruments inside cavities, by way of illustration the stomach, bladder, intestines, etc., improved diagnosis can be conducted using the invented stereo endoscope due to the spatial view of the entire interior side of the tube-shaped cavities such as intestinal vessels.
According to the present invention, the solid state image-recorder system attached to the distal end of the endoscope is provided with at least two image recorders which are essentially composed of a lens and a light-sensitive solid state image sensor, by way of illustration a CCD array. The image recorders, which are allocated in pairs, are placed in relation to each other in such a manner that at least the optical axes of the lenses include a convergence angle which can be set, by way of illustration, via controllable micro-setting elements. Changing the convergence angle permits, by way of illustration, varying within a certain range the distance between the lens plane and the distant point at which the vision fields of both image-recording systems overlap. Thus, the surgeon is able to adapt the spatial imaging qualities of the optical system optimally to the distance region in front of the lens plane on which the viewing interest is focused, by way of illustration due to a planned surgical procedure using other endoscopic instruments.
A preferred embodiment of the present invention also provides for being able to change the stereo base of the image recorder in such a manner that the spatial viewing qualities can be adapted to the current conditions of the field of vision.
Preferably exits of light conductors, which are disposed in the view direction of the solid state image-recording systems, are used for illuminating the to-be-viewed incorporal areas of the body. Furthermore, a symmetrical arrangement of the light exits about the image-recording systems permits homogeneous illumination which is, in particular, a necessity for stereoscopic images.
Having the image recorders, at least however the solid state image sensors, mechanically disposed perferably on a single conductor plate has proven to be especially advantageous. Such a combination prevents an undesirable maladjustment and ensures undisturbed transmission of the image signals obtained by the image recorder which are converted into electric signals by the solid state image sensors and conducted on along the endoscope shaft via respective lines to a proximally attached video-image processing unit.
The electronic triggering of the solid state image sensors in the form of suited periodic signals, which are necessary for perfect functioning of the sensors, and the delivery of the supply voltage can be conducted for two or more sensors via identical signal lines respectively supply lines because the required input signals for the solid state image sensors are identical. The use of more than one image recorder, therefore, does not result in doubling the input signal lines. Consequently, a minimum endoscopic cross section can be maintained. Only one output signal line has to be provided per image recorder in order to transmit the video-image data to the proximal end.
It has been proven to be advantageous if the periodic signals required for a periodic readout of the solid state image sensors are processed in an electronic processing unit which is disposed in the distal region of the endoscope shaft.
The individual object fields recorded by two image-recording systems are converted as previously discussed into electric signals and conducted on to a proximally attached control, processing and representation unit. The proximal side control unit generates the periods for reading out the image recorder, the processing unit provides dual-channel further processing of the image signals gained by the image recorder, which are then conducted to a representation unit in the form of video signals.
By way of illustration, the video signals of both image-recording systems are transmitted alternately every 50 times a second onto a monitor. With such a monitor, which is viewed through infrared-beam coupled glasses which are equipped with a fluid crystal layer, both recorded object fields appearing alternately on the screen synchronously to the screen frequency can be viewed with the respective eye. By means of synchronous darkening of the glasses, the right eye perceives the image, by way of illustration, of the right image-recording system and in the next tact the left eye perceives the left image-recording system. With a respectively high image-reproduction frequency, the brain processes the visual data into a three-dimensional image. Thus, a three-dimensional image can be generated according to the previously mentioned xe2x80x9cone monitor shutter principlexe2x80x9d. By looking at the screen, the surgeon can view the procedure inside a cavity without effort or eye-straining use of look-through endoscopes while he/she is working with other endoscopic instruments. Surgery is considerably facilitated by the three-dimensional image on the monitor quasi permitting a direct view through the abdomen wall.
The present invention provides that the distal end region of the endoscope having the solid state image-recording system for stereo viewing is designed as a stereo video probe which can be detached from the instrument and which contains a magnetic element by means of which the probe, e.g., using a second external magnet can be positioned and attached by way of illustration to the abdominal wall. In this way, viewing positions can be assumed which could not be reached with a single endoscopic incision without having to make additional incisions. Once the video probe has been inserted inside the body and been fixed beneath, by way of illustration, the abdominal wall by means of an external magnet, the video probe can be brought to any point beneath the abdominal wall by moving the external magnets.

Endoscope having stereo-lateral-view optics

Abstract: The image-recording system has at least two image recorders, built in a distal region of the endoscope shaft in such a manner that the viewing directon of the solid state image-recording system being approximately parallel to the axis of a proximal part of the endoscope shaft in one position and being perpendicular to it in another position automatically assumed by the distal region.


The present invention provides an improved solid state fermentation device that combines all of the operations of microorganism cultivation (sterilization, inoculation, cultivation, extraction, and post extraction treatment). This solid state fermentation device is modular in nature and operates in a contained manner so that the live microorganisms from the reactor cannot come into contact with the environment and pollute the environment and also so that the environment inside the bioreactor is aseptic. Another aspect of this invention allows fermentation of microorganisms without inhibiting the growth of the microorganism. Specifically, the bioreactor is designed to remove heat that accumulates inside the bioreactor during fermentation by conduction. Additionally, there is a mechanism to add fluid to the interior of the bioreactor that permits equal distribution and precise control of a variety of environmental parameters. For example, the bioreactor of the present invention provides a means to add nutritive media to the microorganisms at any time during the fermentation process without disturbing the fermenting microorganisms. Furthermore, the bioreactor of the present invention provides a mechanism to mix the contents of the bioreactor at any time and for any duration during the fermentation process. Finally, the present bioreactor provides a means of extracting desired microbial products from the bioreactor without opening the bioreactor.

Solid state fermentation has been practiced for centuries, most often in connection with food production, and can be defined as a technique for growing microorganisms, such as fungi, yeast and bacteria, on moist solid substrates. In recent years, there has been a resurgence of interest in solid state fermentation and its applicability to the production of enzymes, metabolites and organic compounds. Solid state fermentation devices provide several advantages over the commonly used process of submerged fermentation in product yield, cost and ease of use. Despite their economic advantages, the commercialization of solid state fermentation devices for industrial use has been limited for lack of efficient and practical designs.
A wide variety of solid state fermentation devices have previously been described (for review see, Larroche et al., xe2x80x9cSpecial Transformation Processes Using Fungal Spores and Immobilized Cellsxe2x80x9d, Adv. Biochem. Eng. Biotech., (1997), Vol 55, pp. 179; Roussos et al., xe2x80x9cZymotis: A large Scale Solid State Fermenterxe2x80x9d, Applied Biochemistry and Biotechnology, (1993), Vol. 42, pp. 37-52; Smits et al., xe2x80x9cSolid-State Fermentation-A Mini Review, 1998), Agro-Food-Industry Hi-Tech, March/April, pp. 29-36). These devices fall within two categories, those categories being static systems and agitated systems. In static systems, the solid media is stationary throughout the fermentation process. Examples of static systems used for solid state fermentation include flasks, petri dishes, trays, fixed bed columns, and ovens. Agitated systems provide a means for mixing the solid media during the fermentation process. One example of an agitated system is a rotating drum (Larroche et al., supra).
A major problem in both static and agitated solid state fermentation systems is obtaining efficient removal of heat that is generated during the fermentation process. One method of heat removal employed by numerous solid state fermentation systems is aeration. The disadvantage of using aeration as the means of heat removal is that not only is heat removed, but water is also evaporated from the solid matrix, leading to desiccation of the substrate. Constant aeration also makes it more difficult to maintain a stable environment inside the bioreactor with respect to oxygen and carbon dioxide concentrations. Another means of avoiding heat build up is mixing the substrate bed. Unfortunately, mixing during fermentation leads to damage of the cells and gross aggregation of substrate particles. Aggregation of substrate leads to inhomogeneities in local substrate temperature resulting in local differences in biomass growth and activity. These problems are compounded in the large scale systems often required for industrial preparation of certain products. The large scale practice of solid state fermentation using the devices available in the art has the additional disadvantage of being labor intensive.
The steps involved in solid state fermentation include, 1) sterilization of the cultivation device and the cultivation media, 2) inoculation of the cultivation media with the microorganisms, 3) cultivation of the microorganisms 4) extraction of biological products from the cultivated microorganisms, and 5) post extraction treatment of the waste materials and the cultivation device. It is also desirable that the cultivation system provide a mechanism whereby the growth environment during the cultivation process is precisely controlled such that specified conditions are maintained throughout the cultivation process. None of the devices available for solid state fermentation to date provide for carrying out all of the steps required for solid state fermentation in a single fermentation device. Up to now, the practice of solid state fermentation has involved carrying out multiple manipulations which are both tedious and impractical. Such manipulations often risk exposing the cultivation environment to contaminants from outside the cultivation environment, preclude the ability to efficiently and precisely control the cultivation, and lead to reduced product quality and/or yield.
There exists a need for a compact reactor that combines all the operations involved in solid state fermentation into a single device capable of operating in a contained manner and controlling the environment within the bioreactor without inhibiting growth of the microorganism. Furthermore, there exists the need for a device that will allow homogeneous addition of chemicals and nutrients to a bioreactor without contamination.
The present invention provides an improved solid state fermentation device for the cultivation of microorganisms. In general, the invention provides a bioreactor and a process for using the bioreactor for the cultivation of microorganisms on solid media. The Applicants herein refer to the bioreactor of the present invention as a PLAFRACTOR(trademark). In preferred embodiments, the invention provides a bioreactor that is modular in nature and carries out all of the processes of solid state fermentation in a single, contained environment. The modular nature of the bioreactor allows the size of the bioreactor to be adjusted to suit the user""s need. The construction of the bioreactor allows solid state fermentation to be carried out in a manner such that the fermenting microorganisms are kept isolated from the outside environment during the course of the fermentation process. In certain preferred embodiments, the environment inside the modules is precisely controlled to meet specified conditions.
One aspect of the bioreactor is a mechanism to remove heat that accumulates inside the bioreactor during fermentation by conduction. Specifically, the bioreactor is constructed by stacking individual modules. The modular construction of the bioreactor provides multiple modules stacked on top of one another, each with a base connected to a frame for holding the solid medium in isolation from the exterior environment. The base plate of the bioreactor has multiple channels, called non-communicating channels, that carry heating and cooling fluids sandwiched between two sheets. Heat is transferred to and from the modules by conduction. In this way the temperature of the module is precisely maintained to meet the specific requirements of different microorganisms.
Another aspect of the bioreactor is a mechanism to add fluids to the interior of the modules. In this embodiment, the base of the module mentioned above contains a second set of channels, called communicating channels, to deliver fluids to the inside of the module thereby providing a way to adjust the moisture and oxygen content within the bioreactor. For example, for optimum growth, some microorganisms require high carbon dioxide concentrations. Another aspect of this embodiment provides a mechanism by which compounds of interest can be extracted from the microorganisms. For example, extracting fluids can be sent through the communicating channels for extracting the compound of interest for collection. In yet another aspect of this embodiment, the communicating channels can send steam, gas (e.g., ethylene oxide or ozone), or chemicals (e.g., beta-propiolactone, hydrogen peroxide or pyrocarbonic acid diethyl ester) into the bioreactor for sterilization of the bioreactor and its contents before and after fermentation. A final aspect of the present invention is that materials, (e.g., chemicals and/or nutrients), can be added to the bioreactor while the bioreactor is in operation.
In a further embodiment, the present invention provides a mechanism to mix the contents of the bioreactor. According to the present invention the interior of each module has a mixing arm that revolves about the central axis of the module while rotating. Mixing can be carried out at any point in the fermentation process that mixing is deemed to be appropriate. Preferably, mixing occurs after inoculation of the media inside the bioreactor to evenly distribute the inoculum into the media within the bioreactor.
The teachings of the present invention are particularly applicable to the production and extraction of microbial products. In certain preferred embodiments, the microorganisms produce a biologically useful product that can be extracted from the microorganism in the bioreactor and harvested for medicinal and industrial uses. Some examples of medicinals that can be produced by the present invention are lovastatin and cyclosporin. Product that can be used in industrial applications include the microbial enzyme rennet and peptidase. Any of a variety of microbial organisms may be employed according to the present invention.


An enamel frit which provides improved bonding at stoving temperatures below 800.degree. C. after the frit has been stoved on unalloyed steel which is capable of being enamelled, the frit containing 1 to 6% by weight, based on the total quantity of the frit, of bonding oxides and the other constituents so chosen that the following equation is fulfilled: ##EQU1## in which the deviation from the ratio 1:1:1 is at most .+-.8% for each of the monovalent atoms, divalent atoms and pentavalent atoms.. The enamel frits according to the invention being useful for electrostatic powder application.

1. Field of the Invention
This invention relates to enamel frits for sheet steel with superior bonding at low stoving temperatures, in particular for use on substrates of steel which have not been pickled or nickel plated.
2. Background Information
Base and direct enamel frits have the function of establishing a firm bond between the metal workpiece and the vitreous enamel layer. The enamelling should withstand firing over a wide temperature range, have a smooth, flawless surface and undergo no loss of bonding even after repeated stoving. The development of these enamel frits has hitherto taken place empirically. So-called network forming oxides such as SiO.sub.2, TiO.sub.2, ZrO.sub.2, B.sub.2 O.sub.3 and Al.sub.2 O.sub.3 were combined with network migrators such as Li.sub.2 O, Na.sub.2 O, K.sub.2 O, MgO, CaO, BaO or fluorides and phosphates and varied until the enamels were satisfactory in the required commercial properties such as fluidity, surface tension, thermal expansion, surface quality and bonding. To improve the bonding of base enamels, heavy metal oxides such as CoO, NiO and CuO and occasionally iron oxide, manganese oxide, molybdenum oxide or antimony oxide were added in varying quantities.
For direct enamel frits, the addition of TiO.sub.2 increased the resistance of the enamelling to acid attack, while the addition of ZrO.sub.2 increased the resistance to alkalies.
Molten mixtures of base enamel frits and direct enamel frits containing more than 12 oxidic constituents are therefore no rarity. In all multicomponent systems, their development is difficult to oversee and complicated and therefore expensive. The effect of any one component on certain properties of the frits is rarely proportional to its ratio by weight and is independent of other components. An incremental calculation which is recommended for simple types of glass is only rarely possible, e.g. in the case of thermal expansion, and then only approximately. An added difficulty is that several enamel frits are usually mixed together and inert substances may be added for enamel commercial requirements or reasons of economy.
For conventional two-layered or multi-layered enamelling, frits with different viscosities and melting properties were combined for the base enamel and inert substances were added to facilitate the gas reactions proceeding from the sheet steel.
The base enamels which are viscous and hard at the stoving temperature are described as filling bases, while low viscosity, soft frits which wet readily and are capable of dissolving iron oxides are known as network base enamels. The proportions in which they are mixed and the amount of quartz added depend on the quality of the steel and the thickness of the steel sheet as well as on the stoving temperature and the dwell time. Here again, the proportion of frits and the additives used for the milling process are selected empirically and either accepted or varied under practical conditions. Predictions as to the optimum properties such as compatibility of the frits with one another, bonding to differently cast qualities of steel and flow properties of the slips were rarely possible.

Enamel frits for sheet steel with improved bonding